Measuring the braking system of a vehicle is an important element in ensuring the vehicle is safe to operate. Although individual components of a braking system may be inspected when the system is disassembled, such an inspection does not indicate whether the braking system as a whole is working properly. Therefore, it is desirable to provide a system in which the braking force of the entire braking system of a vehicle may be measured in an environment simulating actual road conditions. It is also desirable to provide a system which can accurately test the anti-skid and spring brake systems of vehicles.
Several on-vehicle brake testing systems have been developed in the past. A typical system is disclosed in U.S. Pat. No. 3,286,517. In that system, the wheel of a vehicle is placed on two spaced rollers. An electric motor drives one of the rollers, causing the wheel to rotate. The electric motor is synchronous, causing it to run at the same speed, but drawing current at different rates depending on the load on the motor. A wattmeter measures the wattage provided to the motor. The brakes of the vehicle are then applied, necessitating additional power to the electric motor to maintain the RPM of the rollers. This power is measured by the wattmeter before and after application of the brakes, and the wattage differential provides a measurement of braking force. Other representative patents disclosing measuring systems employing rollers include U.S. Pat. Nos. 3,365,940, 3,633,412, 2,130,900, 4,158,961, 3,712,126 and 4,577,497.
A major shortcoming of prior devices is that energy differentials resulting from the application of brakes are measured by an electric meter. This has three shortcomings. First, electric meters are not sensitive enough to measure the slight energy changes in such systems. Due to this lack of sensitivity, only very bad braking systems can be distinguished from good braking systems. However, it is desirable to more precisely identify the condition of a braking system. Second, the needles of electric meters often flicker during operation, making an accurate reading impossible. Such flickering is most problematic when testing the anti-skid features of a braking system, because such systems intermittently apply braking force. Third, prior systems do not provide a means for recording the meter readings throughout the testing process, making if difficult, if not impossible, to obtain differential measurements.